Why Falling-film evaporator production capacity was reduced
Author：admin From：未知 Time：2018-11-05 13:36 Views：
Falling film evaporator with evaporation rate quickly, the heating temperature is low, short residence time in the equipment, material and under vacuum decompression evaporation, generally the highest heating temperature between 85 ~ 85 ℃, some lower heating temperature, belongs to the low temperature evaporation, intentionally elements in its utmost to keep the material is not damaged. Therefore, it is more suitable for evaporation and concentration of heat sensitive materials. With the continuous expansion of the application field of falling-film evaporator, the main factors such as the decline of production capacity also appear in the practical application process: the evaporator leakage is serious, and water is stored on the shell side; The liquid distributor is malformed or deformed; The evaporator shell scale is serious. The water temperature of the condenser rises. The application of VN-03-10000 three - effect falling-film evaporator in the production of vitriol was illustrated.
1.Evaporator leakage serious, shell side storage water
Main technical parameters and structural features of the equipment:
(1) material medium: vitamin C liquid;
(2) production capacity: 10000kg/h;
(3) incoming material quality score: 12-15%;
(4) : feed temperature 40 ℃.
(5) pH value: 1.4~1.7. .
Structural features: adopting parallel flow feeding method, final effluent discharge; The thermal compression technology is adopted, that is, the heat pump sucks the first effect secondary steam and increases its temperature pressure as a part of heating heat source. The vacuum degree of the evaporation system is maintained by condensing and vacuuming with the interwall tube condenser and water ring vacuum pump. Ti, TiA1 or 316L are used in the contact part with materials. The effective body, preheater, separator and so on all carry on the heat insulation treatment.
One of the reasons for the decrease of the evaporator production capacity, the decrease of the system vacuum degree, and the rise of evaporation temperature is the leakage of the system and the storage of water in the shell. The main parts of leakage are: connection between the square interface of the separator and the lower body, connection between both ends of the secondary steam pipe and the separator and the effective body, or hungry connection with the preheater and the condenser; In the past, flange connection was used for connection between each effective body and the lower body. Due to the aging of rubber pads, the leakage phenomenon was quite serious. Once the evaporator leaked, the vacuum degree of the system would be reduced. If leakage occurs at the joint between the effective body and the lower body, the downward flow of the feed liquid will be blocked, resulting in serious scaling or coking on the lower end of the falling-film tube or the tube plate, and it is more difficult to detect the leakage point, which has occurred in practice. Second, evaporator shell stored water. Except for small pipe diameter, the water stored in the evaporator shell is caused by leakage at shell or pipeline connection. Minimizing unnecessary flange connection is the current direction of evaporator development.
2 .liquid distributor dislocation
The liquid distributor is the key component of falling film evaporator. At present, the disk distributor is widely used. This distributor has simple structure, uniform distribution and good effect. Charging machine is: the main function of material liquid through holes uniformly distributed on the case assigned to each of the falling film tube, and to ensure that each tube falling film around has uniform wetting of material liquid, material liquid under the action of itself and the secondary steam flow down the wall pipe with liquid membrane evenly heating steam flow and tube outside heat exchange. Normal working current distribution on each hole is at the evaporator pipe plate, if distributor holes in the working process of the dislocation or offset, the material liquid in the tube falling film can produce deviation, even wall material, but the forming line flow down along the pipe wall or downward flow in the tube, unable to form a membrane cannot be completely wetted wall wetting or it will cause fouling or coking, evaporation will reduce a lot, evaporation temperature rises, the second, distributor block can also lead to serious or distribution of the holes appear lower production capacity. The above phenomenon appears in actual work. Therefore, the liquid distributor should be preinstalled before delivery, inspected, and unpacked and transported. If it is necessary to be disassembled in the production process, it should not be put in the wrong position.
3.Scale formation on evaporator shell
Evaporator in the process of long-term use, especially equipment using intermittent work, falling film tube outer wall and condenser (pipe or plate tube, pipe water) affect the heat transfer, also can produce scale layer will affect the production capacity of the evaporator in different degrees, the domestic most of the shell side of the evaporator is not set to clean interface, so the shell side cleaning is also more difficult. The proper cleaning method is: soak with 3% sodium hydroxide or oxalic acid in the shell, and the soaking time is not less than 6h.
4. Influence of condenser
The cooling water and water temperature of the condenser are the important parameters of the design evaporator. The lack of cooling water or the increase of cooling water will directly lead to the increase of evaporator's evaporation temperature and decrease of evaporation. The user must be able to provide local and accurate cooling water parameters. Vary widely in the north and the cooling water temperature, and circulating water, even the same evaporator evaporation of the same kind of material in the north and the south its evaporation parameters will have change, the evaporator of the cooling water is set to water, to keep the system stable vacuum degree, the cooling water temperature cannot have larger fluctuation, evaporation cooling water temperature stability parameter is stable, therefore, must to circulation pool added cold water on a regular basis to maintain the basic stability of the cooling water temperature. The installation height of falling-film evaporator and the installation height of the condenser are both high, the water intake of the condenser is certain, and the quantitative water supply is also required. Need of special note is that if the production workshop is must consider whether the evaporator cooling water pipe water supply enough, if you can't meet the separate water supply should be considered, in the past due to pipe water supply cooling water from the cooling water shortage, resulting in evaporator of low water outflow condensation secondary steam to reduce, evaporation temperature, evaporation fell sharply example is seen. Second is the condenser descaling, the most common phenomenon. Tube wall scale increases the heat transfer effect reduces, will also reduce evaporation. Therefore, the condenser should be inspected irregularly, irregularly for pickling or alkaline washing.
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